class Solution {
  public int diagonalSum(int[][] mat) {
    int sum = 0;

    for (int i = 0; i < mat.length; i++) {
      sum += mat[i][i];
      sum += mat[i][mat.length - 1 - i];
    }

    if (mat.length % 2 == 0) {
      return sum;
    }

    else {
      return (sum - mat[mat.length / 2][mat.length / 2]);
    }
  }
}